1. Field of Invention
The invention relates to, generally, a method for building a magnetic core including laminations that are bound into packs for an electrical machine and, particularly, a rotating electrical machine for auto-traction.
2. Description of Related Art
Electric traction combined with traditional thermal traction to obtain hybrid traction is becoming increasingly popular in road vehicles. Electric traction requires the use of at least one rotating electrical machine that is normally reversible (i.e., that may operate both as electric motor by absorbing electrical power and generating mechanical driving torque, and as an electric generator by absorbing mechanical energy and generating electrical power) and is mechanically connected to the driving wheels of the vehicle by a transmission thereof.
One of the requirements by auto manufacturers wanting to make road cars with hybrid traction is a low dispersal of the nominal features of the rotating electrical machines, i.e., that the nominally identical rotating electrical machines also have the same actual features (obviously within a margin of tolerance that is to be the smallest possible). The constancy of the actual features of the nominally identical rotating electrical machines allows road vehicles with true performances to be made that are substantially equal to the nominal performances (i.e., the performances expected by the final customer). Moreover, the constancy of the actual features of nominally identical rotating electrical machines allows the control strategy of the electric traction system to be made more effective and reliable because the behaviour of the main object to be controlled (i.e., the rotating electrical machine that performs the electromechanical interaction) is more easily and accurately predictable.
However, it has been noted that by following the regular construction techniques of rotating electrical machines, the dispersal of nominal features is relatively high, and one of the most important elements determining such a dispersal is the variability of the ferromagnetic features of the magnetic core.
United States Patent Application Publication 2010/154968A1 describes a method for building a magnetic core consisting of laminations bound into packs, for an electrical machine; the building method provides: stacking a group of laminations one on top of the other to build the magnetic core; pre-compressing the group of laminations by a pre-compression press; measuring the actual axial length of the group of laminations while the group of laminations is compressed by the pre-compression press; comparing the actual axial length of the group of laminations with a desired axial length of the group of laminations; and, if the actual axial length is different from the desired axial length (while taking into consideration building and measurement tolerances), adding or removing a single lamination from the group of laminations and therefore repeating the above-described measuring cycle.
However, the building method proposed in U.S. Patent Application Publication 2010/154968A1 has various drawbacks because it requires a very long time to make the magnetic core, it may not be automated (i.e., it always requires manual intervention by an operator), and it could result in damaging the insulator between the laminations with a consequential increase, even significant, of losses of power due to eddy currents in the magnetic core during the operation of the electrical machine (i.e., a worsening of the energy efficiency of the electrical machine).
Thus, there is a need in the related art for a method for building a magnetic core including laminations bound into packs for an electrical machine that does not have the drawbacks described above. More specifically, there is a need in the related art for such a method that does not require a very long time to make the magnetic core, may be automated (i.e., it does not always require manual intervention by an operator), and does not result in damaging the insulator between the laminations with a consequential increase, even significant, of losses of power due to eddy currents in the magnetic core during the operation of the electrical machine (i.e., a worsening of the energy efficiency of the electrical machine). There is a need in the related art for such a method that also is easy and affordable to implement.